1. Field of the Invention
The present invention relates generally to an image forming apparatus. More particularly, the invention relates to an image forming apparatus for improving an image quality by controlling toner amount upon supplying with stirring a toner to be used for image formation in a printer, a facsimile machine or a copy machine employing an electrophotographic process using the toner.
2. Description of the Related Art
Conventionally, in an image forming apparatus employed in the printer, the facsimile machine, the copy machine or the like, a toner of fine particles is used as a developing agent. A toner cartridge filled with the toner is loaded within the image forming apparatus for feeding the toner consumed by development by means of toner stirring and feeding means to a developing portion. There is significant correlation between the toner and an image quality. Therefore, how to control the toner is an important factor to determine a quality of the image forming apparatus.
Therefore, as a technology for controlling a toner supply amount to the developing portion, there is a system for controlling the toner supply amount constant by controlling a rotation speed of a mixer.
A system for optimizing the toner supply amount to the developing portion at a constant amount by the rotation speed of the mixer encounters a problem. That is, the image forming apparatus includes a low speed apparatus and a high speed apparatus. If rotation speed of the mixer is set adapting to the low speed apparatus, the rotation speed of the mixer becomes excessive if applied to the high speed apparatus to supply an excessive amount of toner to the developing portion to cause degradation of the toner to cause defect in the image.
As a measure for this problem, there is a technology for optimizing toner amount to be supplied upon application for the high speed device, a gear train is modified to set the rotation speed of the mixer for feeding the toner at the same condition as the low speed device. However, in this case, specifications of the gear trains inherently become different between the low speed device and the high speed device to make it impossible to use the gear train in common between the low speed device and the high speed device. This results in increasing of kinds of parts to be a cause of cost-up.
On the other hand, as a technology for performing toner control, in Japanese Unexamined Patent Publication No. Heisei 11 (1999)-24513, a dedicated motor for supplying toner is provided for driving the stirring and feeding vane (mixer) to estimate a remaining amount of the toner by integrating a total operation period of the toner supply motor or by measuring a period required from starting toner supply to re-detection of presence of toner by a remaining amount sensor so that the toner supply period is set at a short period when the remaining amount of the toner in the toner cartridge is large, and the toner supply period is set at a long period when the remaining amount of the toner is small. Namely, in the disclosed technology, by employing a variable toner supply period, substantially a constant amount of the toner is discharged.
The system for controlling the toner supply amount constant by controlling the rotation speed of the mixer cannot make the components in common between the low speed device and the high speed device in the image forming apparatus to increase kinds of the parts to result in cost-up.
A technology for controlling the toner amount disclosed in Japanese Unexamined Patent Application No. Heisei 11-24513 estimates the remaining amount of the toner from the total operation period of the motor or the detected period of the remaining amount sensor for discharging the toner by determining the toner supply period on the basis of the remaining amount of the toner to make the toner supply amount substantially constant. However, this technology is not possible to control the toner amount in the developing portion finally influencing to the image quality.
Also, since the dedicated motor is provided for rotatingly driving the stirring and feeding vane (mixer) for supplying toner, the dedicated motor has to be controlled independently and asynchronous with image forming operation to make control complicate resulting in cost-up.
An object of the present invention is to provide an image forming apparatus which can easily control toner supply without degrading compatibility of a toner cartridge in a low speed device and a high speed device, can control a toner amount in a developing portion avoiding feeding of the toner in an excessive amount and whereby avoiding degradation of toner due to supply of excessive amount of the toner using a motor for image forming operation without requiring a dedicated motor for supplying toner.
According to the first aspect of the present invention, an image forming apparatus comprises:
a hopper portion storing a toner;
a mixer rotatably supported within the hopper portion;
a developing portion provided adjacent the hopper portion and constituted of a developing roller and a toner layer restricting member;
a photoconductor supplied the toner from the developing roller for performing developing;
a charge roller for uniformly charging the surface of the photoconductor;
a cleaner portion collecting a residual toner on the surface of the photoconductor and constituted of a cleaning blade and a waste toner collector; and
a plurality of toner amount detectors provided in the developing portion at mutually different height positions.
According to the second aspect of the present intention, an image forming apparatus comprises:
a hopper portion storing a toner;
a mixer rotatably supported within the hopper portion;
a developing portion provided adjacent the hopper portion and constituted of a developing roller and a toner layer restricting member;
a photoconductor supplied the toner from the developing roller for performing developing;
a charge roller for uniformly charging the surface of the photoconductor;
a cleaner portion collecting a residual toner on the surface of the photoconductor and constituted of a cleaning blade and a waste toner collector;
a motor to be rotational driving source for rotatingly driving the developing roller, the photoconductor and the mixer;
a first gear train transmitting rotational driving force of the motor to the developing roller and the photoconductor;
a second gear train transmitting rotational driving force of the motor to the mixer;
a first toner amount detector provided in the developing portion;
a second toner amount detector provided in the developing portion at an installation height different from that of the first toner amount detector;
a first toner amount control portion controlling the first toner amount detector; and
a second toner amount control portion controlling the second toner amount detector.
The first gear train may consist of a first gear, a second gear, a third gear, a fourth gear, a photoconductor gear and a developer gear.
The second gear train may consist of a first gear, a second gear, a fifth gear, a sixth gear, a mixer driving gear and a mixer gear.
The fifth gear may have an electromagnetic clutch and has a two speed gear.
The first toner amount control portion may be connected to the electromagnetic clutch and controls the electromagnetic clutch.
The first toner amount detector and the second toner amount detector may be arranged in parallel to each other in opposition to the developing roller.
The first toner amount detector may be arranged at an upper side of the second toner amount detector.
The first toner amount detector and the second toner amount detector may be formed of a metal rod.
The first toner amount control portion may connect the electromagnetic clutch in response to a signal from the first toner amount detector for operating the second gear train for driving the mixer to rotate to stir the toner.
The second toner amount detector may detect presence or absence of toner in the hopper portion.
The second toner amount control portion may output a toner empty signal of the hopper portion in response to a signal from the second toner amount detector.